1. Field of the Invention
The present invention relates to a video recording/reproducing apparatus for recording and reproducing a video signal, and, more particularly, to a video recording/reproducing apparatus for use in electronic edit.
2. Description of the Related Art
In producing a work or program using a video recording/reproducing apparatus, it is likely that data recorded on a recording medium by this apparatus is properly edited to complete the work or program. Particularly, with the above video recording/reproducing apparatus for professional use, e.g., for preparing broadcasting, commercial and educational works or programs, edit is one of the essential processes. In present video recording/reproducing apparatuses for professional use today, it is typical to use a rotary head type video tape recorder (VTR) for effecting data recording/reproducing on a magnetic tape as a recording medium by a rotary video head, and most of the apparatuses have an editing function.
In a video tape recorder, an editing operation, called Electronic Edit, is generally performed. In principle, the electronic edit is carried out by erasing portions of video and audio signals, which have already been recorded on a magnetic tape, part of the way and then recording new video and audio signals on the erased region on the magnetic tape.
In result of such edit, discontinuity of a signal occurs mainly around the edit entrance point. Particularly, discontinuity of the phase of a video signal causes disturbance on a video display screen and significantly deteriorates the quality of a video image.
To reduce the phase discontinuity of a video signal occurring on a magnetic tape in edit, conventional video tape recorders with an editing function for professional use generally utilize the following two methods.
(a) In initiating the edit, the rotational phase of a video head drum is compared with the sync signal of an input video signal that is to be newly recorded and the rotation of the video head drum is servo-controlled in such a way that the drum rotates in synchronization the sync signal of the input video signal.
(b) The magnetic tape having video signals already recorded thereon is reproduced from the position before the edit entrance point, the vertical sync signal in a reproduced video signal acquired in this reproduction period (called a preroll period) is compared with the vertical sync signal in the input video signal, and the rotational phase of the video head drum is servocontrolled in such a way that both of the vertical sync signals are synchronized with each other and the phases of these vertical sync signals coincide with each other.
The first method (a) is influenced by a mechanical mounting error of a tach pulse generator, which detects the rotational phase of the video head drum and generates a tach pulse in accordance with the detected rotational phase, with respect to the mounting position of the video head in the drum. In other words, with the magnetic tape being previously recorded by another video recording/reproducing apparatus, the phase of the video signal already recorded on the tape cannot accurately be coincident with the phase of a newly-input video signal, so that a significant phase discontinuity is more likely to occur in edit. As a solution to this problem, a tach phase controller (e.g., trimmer) for controlling the phase of a tach pulse indicating the rotational phase is normally adjusted for each edit to compensate for the mounting error so that the phase discontinuity of the video signal around the edit entrance point does not result in a large disturbance on the display screen.
As the second method (b) compares the phase of a video signal reproduced from a previously-recorded magnetic tape directly with that of an input video signal and controls the rotational phase of the video head drum based on the comparison result, the phase discontinuity of the video signal occurring in the edit is improved as compared with the method (a).
However, either method involves servo-control of the rotational phase of the head drum and thus has the control response speed and response accuracy limited.
According to the editing technique in conventional video recording/reproducing apparatuses, therefore, due to the limitation of the response speed and response accuracy of the servo control, it is difficult to always attain a good phase continuity of a video signal at the time of edit.